1. Field of the Invention
The present invention relates to an electronically-controlled fuel injection system for internal combustion engine in which the amount of fuel supplied to the engine is controlled by the duration of the opening of electromagnetic fuel injection valves or the duration of fuel injection, and more particularly the invention relates to such an electronically-controlled fuel injection system designed to improve the mode of fuel injection during the starting periods of an internal combustion engine.
2. Description of the Prior Art
A known electronically-controlled fuel injection system of the above type includes, for the purpose of ensuring an improved starting performance during the time that the cooling water temperature of the engine is low, one or a plurality of electromagnetic cold starting injectors which are mounted in the intake manifold remote from and upstream of the engine cylinders in addition to the electromagnetic fuel injection valves mounted in the respective engine cylinders (the main injectors), and a thermo-time switch which maintains the injection time of the cold starting injectors in relation to the time and the temperature and which renders the cold starting injectors inoperative during the continued rotation of the starter motor to prevent misfiring of the spark plugs.
This prior art system is disadvantageous in that the use of cold starting injectors and a thermo-time switch which are complicated in construction and expensive, is required only for engine starting purposes, and moreover the provision of fuel lines to the cold starting injectors and the electrical wiring of the thermo-time switch not only increases the manufacturing cost of the system but also makes the maintenance of the system difficult.
Another disadvantage is that since the system is designed so that during the starting period a very great amount of fuel is injected in the intake manifold of the engine and only a part of the fuel is vaporized and drawn into the cylinders thus starting the engine, after the engine has started some of the fuel still remains in the intake manifold of the engine so that after the completion of the starting the remaining fuel is gradually drawn into the engine, thus increasing harmful exhaust emissions (in particular, the amount of HC in the exhaust gases).